The present invention concerns an improved non-reciprocal phase shifter structure having a wide band (more than 2 octaves) which operates in the microwave band (1 GHz to several tens of GHz) based on a propagation according to a non-reciprocal surface mode.
Recent theoretical studies on propagation modes for electromagnetic energy in a slab of gyromagnetic material, such as the article published in the review "Cables et Transmission" (Octobre 1973, pages 416-435) by Messrs COURTOIS, CHIRON and FORTERRE, have shown the existence of two TE modes designated respectively by the terms magnetostatic mode and dynamic mode, the latter often being referred to as "edge mode" in the literature. The dynamic mode exhibits the characteristic of a theoretically infinite bandwidth and a non-reciprocal character, which are utilized in the phase shifters of the invention. Referring to the notations of FIG. 1 which illustrates a slab of gyromagnetic material associated with a trirectangular reference O, x, y, z, subjected to a magnetizing field H.sub.o along Oz, in which the energy is propagated along Oy, the dimension of the slab in this direction being assumed to be infinite, the dynamic TE.sub.oo mode is characterized by the following conditions:
______________________________________ Electric field Magnetic field ______________________________________ E.sub.x = O ##STR1## E.sub.y = O ##STR2## E.sub.z = A H.sub.z = O ______________________________________
where
A is a constant
k.sub.x and k.sub.y are the wave numbers=2.pi./.lambda.
K and .mu. are the components of the permeability tensor
.mu..sub.eff is the effective permeability of the material.
The energy in this mode is concentrated along one edge or the other of the ferrite slab in the direction of propagation.
The present invention consists of means intended to modify the conditions at the limits of the volume in which the energy is propagated, so as to obtain a differential phase shift which remains constant in a frequency band larger than 2 octaves.
It is well known (see in this connection the aforesaid article and the article published in Transactions of the MTT Group of the Institute of the Electrical and Electronic Engineers issued of May 5th, 1971, by M. E. Hines) to establish "a magnetic wall" on one of the sides of the central conductor.